Recently, in a conventional solid-state image capturing device such as a CCD image sensor or CMOS image sensor, the reduction of the size of a pixel cell have been extensively performed. In particular, in a CMOS image sensor, in order to reduce the size of a pixel cell, the reduction of the number of transistors required per pixel has rapidly progressed by having a plurality of photodiodes (light receiving sections; photoelectrical conversion sections) sharing one output amplifier.
Herein, first, a case will be described with reference to FIG. 14 in which one output amplifier is provided for one photodiode, and photodiodes are arranged at even intervals in a matrix in a row direction and a column direction. Next, a case will be described with reference to FIGS. 15 to 17 in which one output amplifier is shared by two photodiodes, and the locations of photodiodes are different according to a sequence.
FIG. 14 is a longitudinal cross-sectional view schematically showing an exemplary essential structure of a pixel section in a conventional solid-state image capturing device 100.
In the conventional solid-state image capturing device 100 in FIG. 14, a microlens 2 is arranged above each photodiode 1 making up a pixel so as to correspond to the photodiode 1. Light of an image that is incident on pixels is focused by microlenses 2, and then it is incident upon photodiodes 1. The incident light upon the photodiodes 1 is photoelectrically converted at the photodiodes 1.
FIG. 15 is a longitudinal cross-sectional view schematically showing an exemplary essential structure of a pixel section in another conventional solid-state image capturing device 100A.
In the conventional solid-state image capturing device 100A in FIG. 15, the location of each of the adjacent photodiodes 1A is different in each pixel. For example, in a CMOS image sensor or the like, when one output amplifier is shared by a plurality of photodiodes, the locations of adjacent photodiodes 1A are not at even intervals, as shown in FIG. 15. The two adjacent photodiodes 1A in each group are located close to each other. A microlens 2A is provided above a corresponding photodiode 1A making up a pixel. However, the center position of the microlens 2A does not match the center position of the photodiode 1A in a plane view. Light of an image that is incident upon each of the microlens 2A from right above is not focused upon the central portion of each of the respective photodiodes 1A.
Here is shown a case in which the light of an image is incident on the microlenses 2A from right above. In this case, light of an image is incident upon microlenses 2A from right above at the central portion of a light receiving region. However, light of an image is incident upon the microlenses 2A from an oblique direction at a peripheral portion of the light receiving region. Next, this case will be described with reference to FIG. 16.
FIG. 16 is a longitudinal cross-sectional view schematically showing the light focusing characteristic of the solid-state image capturing device 100A in FIG. 15 with respect to light incident from an oblique direction.
As shown in FIG. 16, when light of an image is incident upon each microlens 2A from an oblique direction, the light focusing position on a photodiode 1A is different for each pixel. The light cannot be focused upon the central portion of the photodiode 1A. As such, the light receiving sensitivity of the photodiode 1A is reduced. In addition, the light cannot be focused upon the same portion on each of the photodiodes 1A, and the light focusing characteristic is different from each other in each pixel, thus showing a different luminance shading characteristic in each pixel.
In order to solve such problems, for example, Reference 1 proposes a conventional solid-state image capturing device to be described below. This will be described with reference to FIG. 17.
FIG. 17 is a longitudinal cross-sectional view schematically showing an exemplary essential structure of a pixel section in another conventional solid-state image capturing device 100B disclosed in Reference 1.
In the conventional solid-state image capturing device 100B in FIG. 17, the location of each of the adjacent photodiodes 1B is different, and the locations of two adjacent photodiodes 1B in each group are close to each other. A common convex-spherical transparent portion 3 is provided for each group of two pixels. Two microlenses 2B are formed on the convex-spherical transparent portion 3 so as to change the light focusing direction inward, so that light of an image can be incident upon the central portion on each of photodiodes 1B.
As described above, in the solid-state image capturing device (CCD image sensor) 100B having photodiodes 1B in a two-pixel unit and the locations of the photodiodes 1B in each two-pixel unit are different according to a sequence, the direction of the incident light is bent by the inclination of the surface of the convex-spherical transparent portion 3 provided to cover two-pixels. Thus, the light is more likely to be incident upon the central portion on each of the photodiodes 1B.
Reference 2 discloses another conventional solid-state image capturing device in which one output amplifier is provided for one photodiode, and the photodiodes are arranged at even intervals in a matrix in a row direction and a column direction, similar to FIG. 14. In such a case, adjacent microlenses are attached to each other in order to eliminate a light invalid region due to a gap between the adjacent microlenses.
Reference 1: Japanese Laid-Open Publication No. 2002-270811
Reference 2: Japanese Laid-Open Publication No. 2003-229550